Mast cells are highly granulated, tissue-resident, effector cells of the immune system. They may be activated via their high affinity IgE receptors or by a number of alternate mechanisms. Following activation they secrete a variety of preformed mediators including histamine, proteoglycans, and a range of serine proteases that are active at neutral pH. Two major families of these proteases have been identified: chymases and tryptases, and they represent the major protein component of the mast cell.
A role has been proposed for mast cell tryptases in the development of a number of inflammatory diseases, including diseases of the respiratory tract, such as asthma and allergic rhinitis, rheumatoid arthritis, and inflammatory bowel disease. Despite the underlying causes of these diseases not being fully understood, it is known that the number of mast cells is increased in the airways of patients with asthma, and in the synovial tissue of patients with rheumatoid arthritis.
Accordingly, there is a clear need to elucidate the role of mast cells in inflammatory disease phenotypes and to develop suitable agents for the prevention and/or inhibition of mast cell-mediated inflammation.
There is a wealth of evidence indicating that many mast cell products are pro-inflammatory. However, recent reports suggest that tryptase may be one of the most important in the development of asthma and inflammatory bowel disorders. Tryptases have been shown to inactivate vasoactive intestinal peptide (VIP), one of only two naturally occurring bronchodilators expressed in the airway, and to induce smooth muscle cell mitosis and hyper-reactivity. More importantly tryptase inhibitors inhibit allergen-induced airway hyperreactivity and markers of inflammation. Tryptase also induces IL-8 secretion from airway epithelial cells, so promoting airway inflammation.
Tryptases have thus become the focus of considerable attention, and there exists a need for the elucidation of effective modulators and inhibitors of tryptases which may be used in treating or preventing mast cell-mediated inflammatory diseases.
A major impediment to determining the role of tryptases, and therefore to developing effective modulators, inhibitors and treatments, has been the confusion over how many different functional human tryptases are expressed. A number of tryptase genes are known to be grouped on chromosome 16, mapping to 16p13.3. These include the gene encoding βI tryptase and its allelic partner αII tryptase, the allelic genes encoding βII and βIII tryptase, two allelic variants of a transmembrane tryptase called gamma (γ) tryptase, and two allelic variants of another tryptase originally named “mMCP-7-like” (Pallaoro et al., 1999; Caughey et al., 2000). Of these, cDNAs have been cloned for all loci except for that encoding “mMCP-7-like” tryptase. Recently the cloning of a more distantly related member, epsilon (ε) tryptase, which is approximately 40% similar to the α/β tryptases has also been described (Wong et al., 2001).
The mMCP-7-like tryptase was so named due to homology between its fifth exon and the murine tryptase mouse mast cell protease (mMCP)-7 (Pallaoro et al., 1999; McNeil et al., 1992). Recently it has been reported (Min et al., 2001) that the mMCP-7-like gene is not transcribed. Based on the examination of a number of human tissues and cell lines for transcription of the mMCP-7-like gene, Min et al. reported that mRNA is absent and concluded that the mMCP-7-like gene is a pseudogene. However the present inventors have surprisingly discovered that the human mMCP-7-like tryptase is indeed expressed and have named the gene, and its polypeptide product delta (δ) tryptase.